The present invention relates to a method for the isolation and production of magnesium metal, magnesium chloride and magnesium-based products from the leaching of laterite material, the use of a method for the leaching of laterite material to isolate magnesium-based products, and magnesium-based products which are isolated according to the aforementioned method.
Accordingly, a method is provided which produces magnesium and various magnesium-based products from the leaching of laterite materials.
JP 54155999 describes a method for introducing a gas containing CO2 into a slurry of nickel-containing ore in order to extract magnesium oxide therefrom. The improvement comprises the addition of NaCl to the slurry to facilitate the extraction of magnesium oxide. The slurry is obtained by (1) calcination of nickel-containing ore at 500-800xc2x0 C. or selective reduction-calcination of nickel contained in the ore in order to obtain calcined ore, and the addition of calcined ore to water or (2) heating the ore to 500-800xc2x0 C. for selective reduction-calcination of the nickel contained therein in order to obtain calcined ore, contacting the calcined ore with an aqueous solution of ammonia containing free sulphur in order to extract useful metals such as nickel therefrom, and the addition of resulting extracted residue to the water. In one example, nickel ore was calcined at 500-700xc2x0 C. for one hour. The resulting calcined ore was added to an aqueous solution of 1 g/l NaCl in order to obtain a slurry. The waste gas containing 10% CO2 was introduced into the slurry to extract magnesium oxide therefrom.
WO 81/02153 describes the production of magnesium oxide of high purity and high surface area. A method is described for the production of MgO from a solution of metal sulphate including MgSO4 which comprises precipitating metals from the solution other than Mg, such as hydroxides, separating the solution from the precipitate, concentrating the separated solution to a specific gravity of from about 1.35 to 1.5 so that impurities including calcium sulphate are precipitated, separating the concentrated solution from the precipitate, isolating the dehydrated MgSO4 crystals from the concentrated solution and decomposing the dehydrated MgSO4 crystals in order to form MgO. Accordingly, a method is described for refining magnesium and nickel-containing ore comprising grinding the ore, preparing a solution of ground ore in sulphuric acid containing less than 10% water, adding water to the slurry of acid-ore in an amount effective to initiate a sulphating reaction, using the heat in the sulphating reaction to heat the slurry of acid-ore, whereby water-soluble metal sulphates and insoluble residue are formed. Leaching the sulphating product with water to extract water-soluble metal sulphates in solution, followed by separation of the metal sulphate solution from the insoluble residue. Metals other than Mg are then precipitated as hydroxides. The solution is separated from the metal hydroxide precipitate, and the solution is concentrated sufficiently to precipitate CaSO4. The concentrated solution is then separated from the precipitate and dehydrated MgSO4 crystals are isolated from the concentrated solution. Dehydrated MgSO4 crystals are broken down to form MgO having a controlled surface area.
DE 2906808 describes a method for isolating nickel from laterite ore, especially having a high magnesium content. This is done by leaching with sulphuric acid whereby the separated leaching solution is neutralised and the heavy metals are separated from the solution. The magnesium sulphate containing solution is at least partly evaporated and the crystallised magnesium sulphate separated. The separated magnesium sulphate is heated in a reduced atmosphere during the formation of sulphur dioxide, water vapour and magnesium oxide, and sulphuric acid is produced from derived sulphur dioxide and is fed back into the leaching step.
U.S. Pat. No. 5,571,308 describes a method for isolating nickel from laterite ore containing large quantities of magnesium and iron. The ore is referred to as saprolitic ore and is subjected to leaching with a mineral acid from the group consisting of HCl, H2SO4 and HNO3. After leaching with HCl, the solution is separated from undissolved solid substances and nickel is preferably isolated by contacting the solution with a resin selective for nickel absorption. The residue contains iron and magnesium chloride which may be subjected to pyrohydrolysis in order to produce their respective oxides and free HCl for recirculation into the leaching system. The nickel is extracted from the resin by using a stripper solution of said acid, and nickel is then extracted from the nickel-loaded stripper solution.
DE 3140380 describes a method for isolating nickel by a sulphuric acid leaching of a nickel-containing oxidic feedstock which also contains magnesium and iron, with the simultaneous production of magnesium oxide and cement. The method comprises reacting the magnesium sulphate containing refinate, at a pH of between 7 and 8.5, a temperature of less than 100xc2x0 C. and a magnesium sulphate concentration of less than 25%, with carbon dioxide and ammonia, wherein magnesium carbonate or hydroxide carbonate, as the case may be, is precipitated and an ammonium sulphate solution is formed. The precipitated product is separated from the ammonium sulphate solution and calcined to magnesium oxide, carbon dioxide being formed. Carbon dioxide is fed back to the precipitation step. A gypsum slurry is formed from the ammonium sulphate solution by adding burned calcium, and ammonia is released. Ammonia is then fed back to the precipitation step. Whilst additives are added, the gypsum slurry is dried and burned to give cement clinker. The sulphur-containing gas which is generated through the cement burning is converted in a sulphur factory to sulphuric acid and which at least partly is fed back into the feedstock leaching.
Consequently, the leaching of laterite material in order to isolate metals is not a new process. However, where nickel-containing laterites are concerned, the target metals from leached laterite materials have to date been nickel and cobalt. The leaching process used to isolate nickel and/or cobalt from nickel laterite ore also dissolves other metal ions. One of these ions is magnesium which is used inter alia in alloying with aluminium. With today""s known technology, the magnesium production is a high-energy process.
Accordingly, the present invention relates to a method for the isolation and production of magnesium metal, magnesium chloride, magnesite and magnesium-based products from the leaching of laterite material, characterised in that magnesium metal, magnesium chloride and magnesite are isolated from any step during the leaching of the laterite material.
According to the method in the present invention, magnesium metal, magnesium chloride and magnesite are isolated after natural magnesium compounds in naturally occurring laterite have been dissolved.
The method according to the present invention is further characterised in that magnesite is produced in any step in the leaching of the laterite material by adding NaCO3 and/or CaCO3 to the leaching solution, after natural magnesium compounds in naturally occurring laterite have been dissolved. The use of a method for the leaching of laterite material to isolate magnesium-based products is also described.
In known laterite leaching processes, magnesium oxide in the laterite material is kept at as low a level as possible because it is deemed to be a cost-increasing element in the processing and is also considered as waste. By using the present method, valuable magnesium-based by-products are produced from any step in the laterite process. The essential feature is to add sufficient acid to cause all the components in the material, including magnesium compounds, to dissolve so that desired ore minerals are then extracted from this solution. The magnesium-based products can be produced from any laterite leaching process. Consequently, the present invention makes it possible to isolate magnesium metal and other magnesium-based products which have previously gone to waste from known processes for leaching laterite material. Owing to the fact that MgO is considered to be an acid consumer in the leaching process and consequently leads to increased costs in the production of nickel and cobalt according to known methods for leaching laterite materials, it is at present kept at as low a level as possible. In the production of magnesium metal from laterite ore according to the present invention, it will be possible for the ore to contain larger amounts of MgO which in turn yield higher amounts of nickel.
Today, acid leaching technology is operated at different pressures and temperatures. In some cases atmospheric temperatures and pressures are used, whilst in other processes elevated pressures and temperatures are employed.
When magnesium is in solution from any of the various leaching processes, the production according to the present invention of identified magnesium products can be carried out.
When magnesium is in solution, according to the invention sodium carbonate (xe2x80x9csoda ashxe2x80x9d) is added and this produces magnesite
MgCO3+H2SO4+H2Oxe2x86x92MgSO4+2H2O+CO2.
MgSO4+Na2CO3xe2x86x92MgCO3+Na2SO4
Below are exemplary embodiments showing examples of methods for isolating magnesium-based products from the leaching of laterite material according to the present invention.